As used herein the term "abnormal tissue" refers to all tissues which have undergone malignant induction such that they may eventually exhibit loss of growth control which is frequently referred to as cancerous or tumorous growth. The detection of the presence of such abnormal tissues is often made difficult because they are located within the body so that until discomfort or other symptoms are experienced by the individual, the existence of the abnormal tissues may not even be suspected. Additionally, present day procedures for early detection can be so expensive and complex as to make their use restricted. Therefore, it would be high advantageous to be able to detect quickly and simply the presence of abnormal tissue, or, ideally, the eventuality of abnormal tissue growth within a body cavity of the host, for example, and preferably the technique should be minimally invasive.
Many forms of cancers or tumors require extended periods of time to achieve a size detectable or injurious to the host, and in some cases this may even take many years. Treatment at this time is considerably more effective when the abnormal tissues are in their early phases and long before they have achieved growth sufficient to cause discomfort or produce detectable symptoms. It would, therefore, also be advantageous to be able to detect the presence of abnormal tissues in their early phases or, even earlier, to detect the tendency for tissues to become abnormal.
Several research efforts have been directed toward discovering the relationship between the electrical impedance of biological tissues and its condition or health. For example, U.S. Pat. No. 3,949,736 discloses that the impedance of biological tissues can provide a useful indication as to whether tissues are healthy or diseased. Specifically, this patent suggests that changes in impedance of biological tissues can be used as a technique for diagnosis of certain carcinomas. According to this patented technique, a low level electric current is passed through the investigated tissue with measurement of the voltage drop across the tissue providing an indirect indication of the overall tissue impedance (i.e., resistance and capacitance). Also, according to this patent, increase in the impedance of the tissue is associated with an abnormal condition of the cells composing the tissue and indicative of a tumor, carcinoma, or other abnormal biological condition of the tissue.
In U.S. Pat. No. 4,729,385 entitled "Probe and Method of Use for Detecting Abnormal Tissues" by R. Juncosa and R. Davies, assigned to the same assignee as the present patent, a special probe is located immediately adjacent to the tissue to be examined (e.g., in the colon) and a second probe is brought into contact with the subject at some other point. The two probes are then incorporated into a bridge circuit and the electrical resistance and capacitance of the examined tissue is determined. It is a fundamental principle of this invention that the tissue capacitance has a direct relationship to the biological condition of the tissue and, more particularly, the capacitance of healthy tissues is substantially greater than that of tissues which are eventually found to develop tumors. The apparatus and techniques disclosed in this prior patent are essentially designed for in vivo use with the specific design of the probes being such that they can be coupled with an endoscope (i.e., colonoscope or other such apparatus) for introduction into an epithelial cavity and thereby locate a measuring probe closely adjacent tissues to be examined.
There are many situations and circumstances where it is neither advisable nor practicable to make direct measurements on the patient itself, but rather instead to take tissue samples which are examined in a labororatory, for example.